The invention relates to improvements in internal combustion engines, and more particularly to improvements in covers for cylinder heads of internal combustion engines. Still more particularly, the invention relates to improvements in sealing means for cylinder head covers and to a method of making such sealing means.
The cover of a cylinder head in an internal combustion engine is attached to the cylinder head by means of fasteners and with the interposition of a so-called cover gasket which ensures that the cavity which is defined by the body of the cover is adequately sealed from the surrounding atmosphere by the establishment of a reliable seal between the marginal portion of the body of the cover and the adjacent portion of the cylinder head. French Pat. No. 1,035,878 to Niquet discloses a cylinder head cover wherein the marginal portion of the cover has a circumferentially complete dovetailed groove for a separately produced sealing gasket constituting a ring with a circular cross-sectional outline. Fastener means are provided to secure the cover to the cylinder head and to deform the ring into sealing engagement with the surfaces surrounding the dovetailed groove and into sealing engagement with the adjacent portion of the cylinder head. The sealing ring is vulcanized to the cover in an operation which follows the placing of the ring into the groove. Thus, the sealing ring is produced as a separate part which is thereupon inserted into the groove of the cover, and the sealing ring is thereupon treated to adhere to the cover. This is a time-consuming and costly operation because it involves the making of a sealing ring independently of the cover, forcing the thus produced ring into the groove of the cover, and additional treatment of the ring in order to ensure the establishment of an adequate seal between the ring and the cover. The sealing action of such gaskets is not entirely satisfactory, especially as concerns the seal between the ring and the cover.
German Offenlegungsschrift No. 31 13 912 of Hemmrich discloses a cover which has a marginal portion with an outwardly extending flange serving to overlie a similar flange on the cylinder head, The flanges are separated by a flat ring-shaped portion of a sealing element which further comprises a U-shaped outer portion serving to partially overlie the two flanges. A ring-shaped clamp is provided to bias the legs of the U-shaped portion against the outer sides of the respective flanges and to thus deform the flat-ring-shaped portion between the flanges. The sealing element can be vulcanized or adhesively secured to the clamp. A drawback of this proposal is that the sealing element and the clamp must be produced in separate machines and must be assembled prior to their application to the flanges of the cover and cylinder head. Moreover, it is necessary to provide the cylinder head with a flange which contributes significantly to the cost of the cylinder head. Still further, and since the clamp must be expanded prior to placing it around the flanges of the cover and cylinder head, it is necessary to greatly expand the sealing element prior to tightening of the clamp around the two flanges. Alternatively, the sealing element must constitute a split ring which presents problems in connection with adequate sealing when the clamp is tightened around the flanges. The utilization of an uninterrupted circumferentially complete sealing ring invariably entails excessive or, at the very least, very pronounced localized stretching and subsequent contraction of the sealing element which affects its sealing action when the cover is affixed to the cylinder head. In order to avoid undesirable and excessive localized stretching and subsequent contraction of the sealing element, it would be necessary to make the sealing element of two or more pieces and to employ a composite clamp with two or more pairs of outwardly extending lugs which are to be secured to each other by discrete screws, bolts and nuts or like fastening elements. Alternatively, the clamp could be provided with several hinges which would contribute to its initial cost and would constitute weak spots as far as the sealing action is concerned. As a rule, a cylinder head cover has a rectangular outline so that it would be necessary to provide at least three hinges.
German Offenlegungsschrift No. 32 16 318 of Skatsche et al. discloses sound absorbing elements (12) each of which includes a rigid inner sleeve (13), a rigid outer sleeve (15) which has a flange (14), and a body (16) of elastic material which is vulcanized between the two sleeves. The sound absorbing elements are secured to yokes (9) by means of screws (17) which extends through the inner sleeves. The just described arrangement cannot provide a fluid-tight seal; it is used solely to reduce the transmission of sound.
Applicant is further aware of German Offenlegungsschrift No. 30 16 673 of Kirchweger which discloses means for reducing the transmission of sound from an internal combustion engine. The cover for the cylinder head deforms a gasket under the action of fasteners which secure the cover to the cylinder head and are surrounded by sound-absorbing rings. The fasteners are simple screws with slotted or recessed heads. This publication does not discuss the mode of making and/or applying the gasket between the cover and the cylinder head.
A drawback of all prior proposals regarding the establishment of a reliable seal between the cover and the cylinder head of an internal combustion engine is that the gasket must be produced as a separate part which is thereupon inserted into a groove of the cover or into a clamp. This contributes to the initial cost of the gasket and/or complicates the attachment of the cover and gasket to the cylinder head. Manual work cannot be avoided so that the afore-discussed prior proposals are not suitable for application in modern production lines wherein the parts of engines are assembled by robots.
Certain other prior proposals involve the provision of a non-elastic gasket which is to be introduced into a groove in the marginal portion of the body of the cover. In order to ensure reliable insertion of the non-elastic gasket, the groove must be at least slightly larger than the corresponding portion of the gasket so that the gasket is a loose fit in the groove and the sealing action of such gasket is nil or unsatisfactory. Attempts to overcome the drawbacks of such non-elastic gaskets include the provision of lateral ribs which project from the gasket and are to overlie the adjacent portions of the cover and cylinder head. The sealing action of such modified non-elastic gaskets is satisfactory only if the surfaces which contact the ribs are machined with a high degree of precision which contributes to the initial cost of the cover and of the cylinder head. When the cover is secured to the cylinder head, the ribs of the gasket undergo permanent deformation so that the gasket cannot be reused. Moreover, the gasket is invariably weakened in regions where it is traversed by the fasteners which secure the cover to the cylinder head so that the sealing action in the regions of the fasteners is less satisfactory or nil. The situation is similar if the marginal portion of the cover is not formed with a groove for a portion of a non-elastic gasket and if the marginal portion of the cover has a flange with holes for fasteners which secure the cover to the cylinder head. In addition, proper centering of a gasket which cannot be inserted into a groove of the cover presents problems and contributes to complexity of application of such cover to a cylinder head.